The present invention relates to a new and improved construction of brake apparatus with variable braking force for cablecars, i.e. cable railway vehicles or aerial cableway vehicles, of the type incorporating at least one pressure-released catch brake and wherein the actual brake or brakes are arranged in a separate brake mount or housing coupled with the traveling carriage of the cable railway or aerial cableway, and furthermore, means are provided in order, following application of the brake, to automatically reduce the brake pressure with increasing coefficient of friction and to increase the brake pressure with decreasing coefficient of friction.
In the construction of brake devices for cablecars, especially aerial cableways, generally for determining the required braking force the coefficient of friction .mu. is considered as a constant value. According to the regulations of the authorities there must be calculated a coefficient of friction of .mu. = 0.1 and the checking and approval of braking devices at aerial cableways is based upon these considerations. In fact, however, the coefficient of friction .mu. is not constant, but fluctuates essentially between 0.05 to 0.3, depending upon the surface properties of the brake elements and the stationary components of the cableway at which the braking effort occurs, in other words in the case of an aerial cableway the support cable or in the case of a funicular or cable railway the rails. It is practically not possible for the stationary cableway component to obtain throughout the entire cableway or track length over a longer operating time a coefficient of friction which is within a very narrow variable range. Also in the case of completely closed support cables there are always present smooth and rough locations. These conditions are naturally taken into account during the determination of the constant calculated value for the coefficients of friction. This leads however to the fact that in most instances the braking force is too large, i.e. the braking effort is much too pronounced. After carrying out the braking effort it then happens that there is a fraying or eroding of the brake jaws during the braking action and later melting away of the brake jaw material. A too pronounced braking action in the case of an aerial cableway represents a danger of overloading the vehicle due to centrifugal acceleration, overloading the traction cable and carrier or support cable, the supports and so forth, i.e. in other words the installation and the passengers are placed in danger. This is also the case for funiculars. In the case where the braking effort is too weak then there is the danger that the cabin will slide.
The dangers existing when the braking effort is too pronounced have been already recognized and previously it has been considered to be desirable to be able to vary the braking force of the braking devices at aerial cableways. Thus, in Swiss Pat. No. 209,254 for instance, there is the suggestion that the magnitude of the braking force or effort can be influenced by the deceleration occurring during braking of the cabin. However, no technical realization of this possibility has really been disclosed in this patent. In the more recent Swiss Pat. No. 292,279 there is described a braking mechanism with variable braking force at aerial cableway vehicles wherein between the traveling mechanism or carriage possessing the conventional clamp brakes and the load container of the vehicle there is interposed a transmission in such a manner that the load container automatically influences the braking force of the clamp brake, and the load container is hingedly connected with the traveling mechanism for a relative displacement in the direction of travel, and the displacement occurring during braking, against the pressure of a spring, brings about by means of the transmission a corresponding closing movement of the clamp brake directly or through the agency of an oppositely directed wedge. In the even more recent Swiss Pat. No. 323,222, there is described a further brake mechanism with variable braking force, in which a separate brake shoe support which is displaceable relative to the aerial cableway in the direction of travel, during the braking action, is automatically pulled by the action of a spring against a wedge closing the clamp. However, practical significance has not been attained by such braking devices with variable braking force. Just as was heretofore the case the construction of braking devices at aerial cableways, as previously mentioned, is predicted upon an assumed constant coefficient of friction. This conception has particularly found usefulness in the case of light aerial cableway vehicles and in such instance is justified. In the meantime, however, the capacity of the cabins of the more recently constructed aerial cableways and therefore the weight of the vehicle has considerably increased, so that the tendency prevails to build even larger aerial cableways with cabins capable of accommodating over 100 individuals. Under these circumstances a brake device possessing a braking force which varies during the braking action corresponding to variable coefficients of friction again becomes actual, since only such braking devices can ensure for a faultless and especially pendulum-free catch brake action and guarantee for the safety of the passengers. The previously mentioned known braking devices of this type, however, are much too inaccurate and too sluggish or inertia-prone in their action, in order to deliver for such type heavy aerial cableway vehicleseven a somewhat reliable braking effort. Just how high are to be placed the requirements regarding safety for a brake mechanism with variable brake force is determined for instance by the fact that a control of the brake force as a function of deceleration- or acceleration values measured by means of an acceleration measuring device, for instance a tachodynamo, driven by a traveling roller, must be considered as cumbersome and impractical since there cannot be eliminated the situation that the traveling roller driving the tachodynamo briefly slides at the support or carrier cable or is raised from the aforementioned carrier cable and just during this time initiates a catch braking action.